1. Field of the Invention
This invention relates generally to sewer and drain cleaning machines and, more particularly, to a coupling device for coupling a cable of a sewer and drain cleaning machine to a cutting tool which is mounted at a distal end of the cable.
2. Background Art
Power driven cables or "snakes" for cleaning out clogged drains or sewer pipes are well known. Generally, an elongated, flexible sewer cable formed of one or more of the helical wires is inserted into a drain pipe to be cleaned and, at the same time, the cable is rotated. A sewer or drain cleaning tool is attached to a distal end of the cable in order to cut away or clear a clogged portion of the drain pipe. A number of different types of cleaning tools can be used depending on the type of obstruction encountered.
A common problem which occurs when using power driven cable is breaking or kinking of the sewer cable due to excessive torque being applied to the cable by the motor drive when the tool encounters an obstruction which severely limits or stops the rotational movement of the tool. In such a situation, severe torque is applied to the cable because the cleaning tool is not rotating at all. The excessive torque causes the cable to permanently kink or break. Should the cable break the expensive cleaning tool is difficult, if not impossible, to retrieve from the sewer or drain pipe. If the cable permanently kinks, it is no longer usable.
Attempts have been made to address this problem by providing a slip clutch at the power-driven end of the sewer snake as shown in U.S. Pat. Nos. 3,742,548 and 3,574,878. The use of slip clutches as described in these patents do not respond directly to the torque at the distal end of the cable which is where torque build up causes kinking or breaking of the cable due to the tool encountering a blockage.
These clutches are mounted adjacent to the motor drive so that they are easily accessible to the operator and may be periodically adjusted to change the torque setting at which they will begin to slip. When a large length of the sewer cable is fed into the sewer or drain pipe, the total weight of the sewer cable to be turned increases and accordingly, more torque must be generated to rotate the sewer cable within the drain pipe. Additionally, as the sewer cable is fed into the drain pipe it encounters many minor obstructions such as bends or turns in the sewer pipe itself which apply additional resistance to rotation of the sewer cable which then demands additional torque to be applied to the driven end of the cable to keep the cable rotating within the drainpipe.
By the time the torque setting has been adjusted to account for the weight of the cable, the setting is so high that the cable will kink or break if the distal end of the cable encounters an obstruction which prevents the tool from rotating.
In U.S. Pat. No. 4,104,754 an overload slip or escapement clutch is positioned between the sewer cleaning head and the adjacent free or distal end of the cable. The slip clutch is spring loaded and gives off a vibrational click when slippage is occurring within the clutch. The vibration provides feedback to the operator that a blockage has been encountered. Such complex slip clutches are known to wear, are unreliable and may provide excessive torque if improperly adjusted.
The present invention is designed to eliminate the above disadvantages of prior art devices and to provide a simple coupling device which is reliable in preventing breakage or kinking of the sewer cable, is easily reset and is inexpensive.